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Choosing Your LC Particle

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We have a lot of options when choosing a column for our liquid chromatography (LC) application. In addition to the stationary phase and the column dimension, we also need to pick the perfect particle. We cover the differences between superficially porous particles and fully porous particles, pore size, and more to give you the information you need to make the right choice.  

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Fully porous or superficially porous? 1.8 or 2.7 µm?  90 or 300 Å? These are only a handful of the choices that are available when you are choosing your LC particle. Superficially porous particles, such as Raptor, feature a solid, impermeable core enveloped by a thin, porous layer of silica that decreases the diffusion path and reduces peak dispersion. This, in combination with other unique properties resulting from the solid core, allows the use of a 2.7 µm superficially porous particle to achieve the performance of a sub-2 µm fully porous particle while generating less backpressure. If that’s the case, why even consider fully porous particles? These particles have more surface area per gram, allowing both additional retention for poorly retained compounds and the ability to inject more mass on column compared to superficially porous particles.

Let’s also consider particle size. For the same column dimension, if the particle size is reduced by half, the plate number doubles.  However, backpressure also increases by a factor of four. Keeping this in mind, the pressure capabilities of your instrumentation should align with your choice in particle size. Pore size is often overlooked when selecting an LC particle. Small-pore particles have pore sizes ranging from 60–150 Å and perform well during separations of small molecules that are less than approximately 1,000 Da. Large-pore particles tend to be used for separation of larger molecules such as proteins. As a general rule, the pore size should be at least three times the size of hydrodynamic diameter of the molecule for easy access to the pores.

Before choosing the particle for your next analytical column, consider the size of your target analytes and whether you need speed, backpressure restrictions, sample capacity, or retention in order to effectively pair your column with your analysis.

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